/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.test.checkpointing.utils;

import org.apache.flink.api.common.functions.RuntimeContext;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.runtime.state.CheckpointListener;
import org.apache.flink.streaming.api.TimeCharacteristic;
import org.apache.flink.streaming.api.checkpoint.ListCheckpointed;
import org.apache.flink.streaming.api.functions.source.RichSourceFunction;

import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;

import java.io.Serializable;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;

import static org.junit.Assert.assertEquals;

/**
 * Source for window checkpointing IT cases that can introduce artificial failures.
 */
public class FailingSource extends RichSourceFunction<Tuple2<Long, IntType>>
	implements ListCheckpointed<Integer>, CheckpointListener {

	/**
	 * Function to generate and emit the test events (and watermarks if required).
	 */
	@FunctionalInterface
	public interface EventEmittingGenerator extends Serializable {
		void emitEvent(SourceContext<Tuple2<Long, IntType>> ctx, int eventSequenceNo);
	}

	private static final long INITIAL = Long.MIN_VALUE;
	private static final long STATEFUL_CHECKPOINT_COMPLETED = Long.MIN_VALUE;

	@Nonnull
	private final EventEmittingGenerator eventEmittingGenerator;
	private final int expectedEmitCalls;
	private final int failureAfterNumElements;
	private final boolean usingProcessingTime;
	private final AtomicLong checkpointStatus;

	private int emitCallCount;
	private volatile boolean running;

	public FailingSource(
		@Nonnull EventEmittingGenerator eventEmittingGenerator,
		@Nonnegative int numberOfGeneratorInvocations) {
		this(eventEmittingGenerator, numberOfGeneratorInvocations, TimeCharacteristic.EventTime);
	}

	public FailingSource(
		@Nonnull EventEmittingGenerator eventEmittingGenerator,
		@Nonnegative int numberOfGeneratorInvocations,
		@Nonnull TimeCharacteristic timeCharacteristic) {
		this.eventEmittingGenerator = eventEmittingGenerator;
		this.running = true;
		this.emitCallCount = 0;
		this.expectedEmitCalls = numberOfGeneratorInvocations;
		this.failureAfterNumElements = numberOfGeneratorInvocations / 2;
		this.checkpointStatus = new AtomicLong(INITIAL);
		this.usingProcessingTime = timeCharacteristic == TimeCharacteristic.ProcessingTime;
	}

	@Override
	public void open(Configuration parameters) {
		// non-parallel source
		assertEquals(1, getRuntimeContext().getNumberOfParallelSubtasks());
	}

	@Override
	public void run(SourceContext<Tuple2<Long, IntType>> ctx) throws Exception {

		final RuntimeContext runtimeContext = getRuntimeContext();
		// detect if this task is "the chosen one" and should fail (via subtaskidx), if it did not fail before (via attempt)
		final boolean failThisTask =
			runtimeContext.getAttemptNumber() == 0 && runtimeContext.getIndexOfThisSubtask() == 0;

		// we loop longer than we have elements, to permit delayed checkpoints
		// to still cause a failure
		while (running && emitCallCount < expectedEmitCalls) {

			// the function failed before, or we are in the elements before the failure
			synchronized (ctx.getCheckpointLock()) {
				eventEmittingGenerator.emitEvent(ctx, emitCallCount++);
			}

			if (emitCallCount < failureAfterNumElements) {
				Thread.sleep(1);
			} else if (failThisTask && emitCallCount == failureAfterNumElements) {
				// wait for a pending checkpoint that fulfills our requirements if needed
				while (checkpointStatus.get() != STATEFUL_CHECKPOINT_COMPLETED) {
					Thread.sleep(1);
				}
				throw new Exception("Artificial Failure");
			}
		}

		if (usingProcessingTime) {
			while (running) {
				Thread.sleep(10);
			}
		}
	}

	@Override
	public void cancel() {
		running = false;
	}

	@Override
	public void notifyCheckpointComplete(long checkpointId) {
		// This will unblock the task for failing, if this is the checkpoint we are waiting for
		checkpointStatus.compareAndSet(checkpointId, STATEFUL_CHECKPOINT_COMPLETED);
	}

	@Override
	public List<Integer> snapshotState(long checkpointId, long timestamp) throws Exception {
		// We accept a checkpoint as basis if it should have a "decent amount" of state
		if (emitCallCount > failureAfterNumElements / 2) {
			// This means we are waiting for notification of this checkpoint to completed now.
			checkpointStatus.compareAndSet(INITIAL, checkpointId);
		}
		return Collections.singletonList(this.emitCallCount);
	}

	@Override
	public void restoreState(List<Integer> state) throws Exception {
		if (state.isEmpty() || state.size() > 1) {
			throw new RuntimeException("Test failed due to unexpected recovered state size " + state.size());
		}
		this.emitCallCount = state.get(0);
	}
}
